Electromagnetic delatching means



Jan. 28, 1958 w. DEANS ELECTROMAGNETIC DELATCHING MEANS 2 Sheets-Sheet 1 Filed Jan. 8, 1954 Zic-...5;

lil

United States Patent O ELECTROMAGNE'HC DELATCHiNG MEANS William Deans, Ridgewood, N. J., assigner to l-T-E Circuit Breaker Company, Philadelphia, Pa.

Application January 8, 1954, Serial No. 402,950

Claims. (Cl. 2043-88) The present invention relates in general to the art of electrical switchgear and more particularly concerns novel electromagnetic latch operating mechanisms.

In its most elementary aspect, a circuit breaker includes a pair of current-interrupting contacts which are normally spring-biased toward the open circuit position. The nature of the mechanism associated with these contacts is, of course, a function of the size and complexity of the breaker and is related to such periormance specilications as current-interrupting capacity, voltage, interrupting speed and the like. Customarily, however, circuit breaker contacts are found associated with apparatus for minimizing the effects of arcing, a contact closing linkage and some contact release mechanism. Whatever the closing mechanism, and innumerable forms have been proposed in the patents and literature, some form of latch is ordinarily utilized to retain the contacts in releasable engagement. Of particular concern in the present application is the tripping mechanism used for automatically releasing this latch under some predetermined electrical condition to permit disengagement oi the aforementioned contact arrangement.

Considerable eiort has been expended in the development of automatic release devices and, in general, these are operative upon the principle that a movement sufcient to release the latch is imparted to some release member whenever the necessary current tripping condition occurs. An elementary example of a current overload tripping mechanism is a solenoid through which the full contact current, or some preselected fraction thereof, is directed. When the current value exceeds the established overload rating of the system, the solenoid armature is activated against a normal spring bias, to delatch the contact tripping mechanism. Solenoids have been used similarly to respond to over or under voltage conditions and, in fact, to any condition considered faulty in the specific electrical system into which the circuit interrupter is incorporated.

Although solenoid trip mechanisms have demonstrated their dependability in countless circuit breakers, certain limitations to their applicability have been well recognized by those responsible for their design and use. ln the usual solenoid, an iron core operates within a currentcarrying coil. The actuating force is developed by the interaction of the ilux generated by the coil and the iron core plunger, and as a practical matter, to achieve the forces requisite in large breakers, comparativelyv large masses of iron have been required. rl`his demand, of course, is inconsistent with a requirement of rapid operation in modern high speed breakers, and as a consequence, solenoid designs usually involve large copper coils to activate the weighty solenoid core.

Another common type of response mechanism is the thermal overload protector. Conventionally, this device comprises a bimetal element arranged for physical distortion under the influence of the thermal effect of overcurrent, and suitable mechanical linkages are ordinarily adapted to transform this configuration change to a delCC latching movement. In numerous commercially available circuit interrupters, a series current solenoid is cmployed to provide instantaneous tripping under conditions of severe overload while thermal elements, though slow in response, serve to insure adequate protection for minor overloads of undue duration.

The present invention has as a primary object the provision of a sensitive device capable of reliably and substantially instantaneously responding to pre-established overcurrent conditions for delatching high speed circuit interrupters. Conceptually, in accordance with the principles of this invention, the load current, as it iiows through the switchgear, is guided through a single movable conductor, which is disposed in non-contacting cooperative relationship with a novel passive magnetic structure. Upon the occurrence of an overcurrent load fault, the magnetic field enclosing the conductor so reacts in the presence of the magnetic structure as to cause displacement of the conductor to delatch the Contact tripping mechanism. It will be observed that motion of this conductor is' only instrumental for delatching purposes and does not require that the conductor itself bear the arcing associated with circuit interruption, despite the fact that the full current flows through it.

ln one aspect of this invention, the magnetic structure mentioned earlier is comprised of an aligned stack of like magnetic members, each formed with a substantially V-shaped, or otherwise tapered opening, or notch; thns dening a V-shaped air gap through which the movable conductor is operative. Particularly noteworthy is the fact that the intensity of magnetic eld surrounding the movable conductor does not depend in any manner on the conductor mass, but is solely a function of load current. Thus, the mass to be set in motion need not exceed that of the minimum conductor size which may safely carry the overload current for the tripping interval.

It is therefore an object of this invention to provide a circuit breaker delatching arrangement utilizing a movable conductor in association with a static magnetic assembly.

Another object of this invention is to provide a novel magnetic structure capable of activating a current-carrying conductor in a particular direction irrespective of whether the current flow is direct or alternating.

A further object of this invention is to provide a latchactivating mechanism operable at exceedingly high speeds due to the low mass of the members to be motivated.

Another object of this invention is to attain maximum electromagnetic effect with a minimum of magnetic material through the use of a novel spacing arrangement for magnetic sheet stock.

These and other objects of the present invention will become apparent from the following detailed specification when taken in connection with the accompanying drawings in which:

Figure l is a plan View generally depicting the structural elements necessary to the latch operating mechanism of the present invention.

Figure 2 is a side View of the apparatus illustrated in Figure l.

Figure 3 is a diagrammatic representation of the principlesof this invention as embodied operationally in simplied circuit breaker equipment.

Figure 4 illustrates a modiiication of the apparatus shown in Figure 3 and is shown applied to a typical circuit breaker.

Figure 4a illustrates the bimetal modification of Figure 4.

With reference now to the drawings and more particularly to Figures 1 and 2 thereof, there is illustrated an arrangement of magnetic and conductive elements from which the fundamental concepts underlying the present invention may be readily deduced. Specifically, there is shown a plurality of identical metallic plates 11 which, for purposes of this invention, are formed of a suitable magnetic substance of relatively high permeability, such as iron, steel or magnetic alloy. As shown in Figure 2, magnetic plates 11 are vertically stacked with aligned edges, and a substantially uniform vertical separation is maintained between plates in the assembly. The specific structure for rigidly retaining the magnetic plates 11 in the orientation shown in these figures has been omitted. But as a representative example, a plastic imbedment extending vertically and enclosing the left-hand edges of the plates will suffice to provide the necessary rigidity and permit attachment to some equipment supporting frame.

As revealed most clearly in Figure 1, each of the like magnetic plates 11 is formed with an opening or notch 12 inwardly tapering from an outer edge 13 of plate 11 to an inner termination at edge 14 in the central region of the plate. ln the embodimentshown, edges 15 and 16, defining the notch taper, are essentially straight lines.

It will become apparent from the discussion to follow that the precise configuration of notch 12 is not itself particularly critical provided that a reasonable taper is maintained. Least critical is the nature of the innermost edge 14, and in fact, edges 15 and 16 may be extended I if desired to intersect and define a V-shaped opening terminating in a point vertex.

Since the magnetic plates 11 in Figures 1 and 2 are each formed to the same pattern, the fabrication problem is rendered quite simple, since the plates may be stamped directly from sheet stock of the desired thickness.

In Figures 1 and 2, an uninsulated cylindrical conductor 21 has been shown disposed within and extending vertically through the notched or V-shaped air gap defined by the stack of magnetic plates 11 having the configuration illustrated. Conductor Z1 is preferably positioned in the region of the open end of the notch and is symmetrically arranged in non-contacting relationship with respect to the taper defining edges 15 and 16.

With all magnetic and electrical components in the relative position shown, let it be assumed that a current I is directed downward through conductor 21 from a source which need not be disclosed since it is not pertinent to the present discussion. Applying conventional engineering designations, the magnetic field established by this downward current flow has been illustrated in Figure 1 as comprised of closed magnetic fiux loops which circumscribe the conductor itself and extend outward with diminishing intensity. Evidently, a portion of this field characterized by flux lines, such as 23, will be wholly disposed within the unit permeability, tapered air gap encompassed by the side walls of the notch. Other ux lines, such as 25, in the magnetic field so generated will, to a large part, extend through the magnetic plate 11 and will be closed through the air gap. From elementary electromagnetic theory, all lines are closed, continuous and non-intersecting, and since each field line must enclosed conductor 21, no line is capable of existing entirely within the magnetic plate 11.

By virtue of the bilateral characteristics of the components employed, reversal of the direction of current I will reverse the direction of the eld, but the over-all field of pattern will otherwise be substantially without change. ln other words, if the current I is in fact a conventional alternating power current, the magnetic field shown will alternately build up in one direction and then the other at line frequency. At any instant of time, the field strength is proportionally related to the current intensity; however, the nature of the relationship is complicated by the complex saturation characteristics of the magnetic material employed, and by the relative dimensions of conductor and notched air gap.

In order to analyze the mutual interaction of conductor 21 and the magnetic material of plate 11, particular til) reference is made to Figure 1. Whatever effect is found applicable to one plate will correspondingly exist for each of the remaining plates in the stack. It is thus possible to consider the reaction of magnetic field and magnetic plate simply as a two-dimensional problem.

From an inspection of Figure l, it becomes apparent that if conductor 21, when carrying current, were to be displaced horizontally and to the left, the effect would be to shorten the lines in the outermost region of the magnetic field established by current I; that is, a larger portion of the held would be confined to the higher permeability magnetic material than in the unit permeability air gap. As a consequence, if magnetic plate 11 is thought of as securely anchored to some reference frame, there is a force exerted on conductor 21 tending to displace it inwardly toward the vertex of the notched portion of the plate, or edge 14. In fact, if conductor 21 were wholly unrestrained, it would move as far into the notch as possible and would ultimately contact the innermost edge 14 thereof,

The magnitude of this displacement force for any one plate is evidently dependent upon a multitude of factors in addition to the magnitude of the current. Among these factors are magnetic plate permeability, relative size of magnetic plate, and size and taper of the notch and current magnitude. The fact that magnetic field intensity is dependent upon current magnitude indicates that the extent of the driving force on conductor 21 will be dependent upon current and this particular feature is of special interest, as will be noted below. The direction of the force effect produced by the current I is entirely independent of the current direction since the tendency to shorten the fringing magnetic eld remains unaltered whether the field rotation is clock-wise or counter-clockwise. As a direct consequence, the effect of an alternating current is to provide a thrust on conductor 21 which pulsates at twice the frequency of current source.

Returning now to Figure 2, it is apparent that the lateral thrust upon conductor 21 upon the application of current I is increased through the utilization of a plurality of stacked magnetic plates 11. Clearly, it is possible to stack plates 11 in direct contact with each other without adverse effect. However, the total force available for a given amount of magnetic substance is materially increased by spacing the plates so as to encompass the field surrounding a greater length of conductor 21.

At this point, an advantage noted in the preceding discussion should be considered more fully. The entire load current flows through conductor 21. Evidently then, this conductor must be of sufficient cross section to permit handling this current on a continuous basis. Again, from elementary magnetic theory, the magnetic field so generated and enclosing conductor 21 through plate 11 is not dependent upon conductor size, but rather solely upon current. Consequently, it is wholly unnecessary to increase the mass of conductor 21 to achieve a greater force effect for a given current. That is, the minimum mass necessary to carry the load without undue temperature rise is that desired for conductor 21, and this will be shown of considerable value in circuit breaker operation.

Having thus described those concepts underlying the development of a force upon a current-carrying conductor by passive magnetic plates, reference is now made to Figure 3 which, in diagrammatic form, depicts the application of these principles to the switchgear art. It should be emphasized at this point that no attempt whatsoever has been made in Figure 3 to illustrate the practical mechanical engineering design features which enterinto the construction of a circuit interrupter, primarily because the principles disclosed earlier in connection with Figures l and 2, and shown incorporated into useful equipmentin Figure 3, are readily adapted to a broad class of equipment. Thus, whatever mechanism is shown in Figure should be considered as representative only of the func'- tional aspects of actual switch-gear and without limitation upon the scope of utility of the invention herein disclosed.

In Figure 3, ythe circuit interrupter is shown to include a contact carrying arm 41 rotatable upon a pivot pin 42, the latter being anchored to some suitable supporting frame. A handle 43 is shown for the purpose of indicating that manual closure of the breaker is possible. Contact 44 is welded or otherwise attached to one end of Contact carrying arm d1 and a mating cooperative contact 4S is similarly fastened to a rigid contact bearing member 4.6. Upon circuit closure as shown in the drawing, a current l flows through the contacts and through the external load circuit protected by this equipment.

Contacts 44 and 4S are biased toward a normal open circuit position by a lrelatively powerful compression spring 51. in the drawing, arm 41 is shown restrained in the closed circuit position by a latch 52 at the upper end of a conductive member 53. It will be observed that the lower end of conductive member 53 is freely pivoted upon rigid pin 54 and that the current I is conducted outward through fixed conductive supporting member 55.

A flexible conductive connection is schematically represented at 56 and functions to preclude current flow interference resulting from any high resistance contact at the pin connection 54.

Conductive member 53 is retained in the position shown against a suitably anchored insulating stop 61, by a tension spring 62 of moderate force. Here again, a tlexible conductor schematically represented at 63 is used to provide a low resistance current path between conductive member 53 and arm 41. But it must be understood that the provision of flexible conductor 63 is made in such a manner as to preclude interference with the normal rotation of contact carrying arm 41 and conductive member 553 about pins 42 and 54, respectively. The function of flexible conductor 63 will be further discussed below.

In the manner heretofore illustrated and described in connection with Figures l and 2, a plurality of identical, vertically spaced notched magnetic plates 11 are positioned astride conductor 53. The physical relationship of conductive member 53 to the plates 11 in Figure 3 is precisely that disclosed in Figure l for plates 11 and conductor 21. In Figure 3, block 72 represents a rigid insulating anchorage and spacer for the stack of magnetic plates 11.

For the circuit interrupter arranged as in Figure 3, the current i in flowing through conductive member 53 establishes a eld as disclosed in Figure 1, but the forces created thereby are insufficient in normal operation to cause motion of member 53. If due to a faulty condition in the external load circuit, a predetermined current overload occurs, there will be established about conductive member 53, a field of such magnitude as to cause the generation of a force thereon tending to draw it further into the notched plates. At such point that the force generated by the overcurrent exceeds the combined restraining force imposed by tension spring 62 and the frictional force developed at latch 52, member 53 will rotate about pivot 54 in a counter-clockwise manner to delatch arm 41. This will be instantaneously followed by counterclockwise rotation of arm 41 about pivot 42 under the iniluence of the full force of spring 51 and will interrupt current I at the junction between contacts 44 and 4S.

It is now clear that ilexible connection 63 is necessary to preclude arcing at the latch 52 during current interruption. It is further clear that since high speed rotation is essential to members 53 and 41, that whatever ilexible arrangement is used must be for current carrying purposes only and must not interfere with mechanical movement. Finally, it should be noted that the point 75 at which dexible conductor 63 joins arm 53 must be above the stack of notched plates 11 in order that the full line current I be 6 directed through conductor 53 in the region of the plates 11.

Upon completion of the interrupting cycle due to an overload, the mechanism shown in the drawing may be relatched by manually or automatically reclosing contacts 1M and 4S. Tension spring 62 will reset the latch for another cycle of operation.

The various features which have been discussed in connection with Figure l are plainly effective in the operation of the device shown in Figure 3. Thus, the force applied, and consequently, the speed of rotation of conductive member 53, are immediate functions of the magnitude of the overload current, which feature is extremely advantageous in circuit breaker operation. Although the instantaneous force tending to actuate member 53 is pulsating in nature when I is an alternating current, its effectiveness is directional as for direct current.

The minimum force required to trip the circuit breaker is, of course, a function of the specific application; but whatever its magnitude, it may be attained by appropriately stacking a sufficiently large number of plates 11, and by adjustment of the initial spacing of conductor and plates.

In another embodiment of my invention, the conductor 21 or 53, respectively, as shown in Figures l and 3 may be a bimetallic element. This modification is shown in Figures 4 and 4a as applied to a circuit breaker of the type disclosed in Patent No. 2,701,284 issued February l, 1955. The circuit breaker 60 is provided with a molding housing 61 having its various components side mounted in appropriate grooves and recesses thereon. A stationary contact 62 is electrically connected to the terminal member 63 by means of terminal conductor 64. The movable contact 65 is secured to the contact arm 66. An arc chute 67 is provided to extinguish the arc created by the separation of the movable contact 65 from the stationary contact 62. The spring 69 is connected at one end of the movable contact arm 66 and at the other end to the U-shaped cradle member 70 and maintains contact pressure when the components are in the position illustrated in Figure 4. That is, the movable contact arm 66 is pivoted in appropriate grooves in the bottom portion of the circuit breaker handle 77 and hence, the spring 69 will bias the contact arm 66 toward the left to thereby maintain high contact pressure.

A pigtail '73 is brazed at one end to the movable contact arm 66 and at the other end to the lower movable portion of the bimetallic element 77. The bimetallic element 77 is brazed at its upper end to the terminal 79. Screw 7S is in threaded engagement with the bimetallic element 77 and terminal 79 provides calibration adjustment. The terminal member 79 is seated in a recess 80 of the molded housing 61 and has a terminal screw 82 secured thereto. Thus, the normal flow of current through the circuit breaker is as follows. From the terminal connector 82, through the terminal 79, screw 78, bimetallic element 77, pigtail 73, to the movable contact arm 66, through the movable contact 65, to the stationary contact 62 and thence through the other conductor 64 to the other terminal 63.

An L-shaped member 90 is secured to the bimetallic element 77 by means of the rivet 91. A cradle 70 is rotatably mounted on the permanent pivot 93. Thus, as seen in Figure 4, the cradle 7i), although biased in a clockwise Idirection around the pivot 93, is prevented from rotating due to the engagement of the cradle surface with the latch surface 96 of the L-shaped latch member 90.

On the occurrence of an over current condition, the bottom portion of the bimetallic element '77 will deect to the right thereby disengaging the latch portion 85, 96 of the cradle 76. lf the current I constitutes only a moderate overload, delatching would be achieved by the relatively slow deformation of the bimetall 77 under the inuence of increased temperature, Notwithstanding this property, a heavy over-load would be followed by instantaneous movement of the bimetallic element 77 to the right in a manner already described in connection with Figure 3 'thereby resulting in rapid disengagement of the cooperating contact 62, 65.

The total independence of the rapid and slow ovenload protection features stems from the fact that the forces on member 53 of Figure 3 or bimetal 77 of Figure 4 are in no way dependent upon substance of which it is made. lt is only dependent upon current therethrough, and hence, the strength of the magnetic eld and its relation to the notched magnetic members. The determination of whether to use a conductive member 53 or 77 of copper, for example, or an iron-brass bimetal strip, is a design choice which must be marde upon consideration of the operational requirements of the circuit breaker.

lt should be apparent that while conductive members 53 and 77, in Figures 3 and 4, respectively, have been shown vertically disposed and positioned within a plurality of horizontally stacked magnetic plates, this is not to be thought of as a limitation to the general utility of the device. The forces imposed by the retaining springs, the frictional latch contacts and the activating overload currents are far in excess of any gravitational forces so that the latter may be overlooked and the relative orientation of components may be changed as needed.

ln the foregoing, l have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specic disclosure herein but only by the appending claims.

l claim:

1. An electromagnetic latch operating mechanism comprising a magnetic member formed with a tapered opening therein and a conductor disposed for movement within said opening relative to said magnetic member, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

2. An electromagnetic latch operating mechanism comprising a magnetic member formed with a tapered opening and a conductor disposed for movement within said opening relative to and in a non-contacting relationship with said magnetic member, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

3. An 'electromagnetic latch operating mechanism comprising a magnetic member formed with an opening in,- wardly tapering from an outer edge thereof and a conductor disposed within said opening for movement relative to said magnetic member, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

4. An electromagnetic latch operating mechanism comprising a magnetic plate formed with a notch tapering inwardly from an outer edge thereof, means rigidly securing said magnetic plate, and a conductor extending through said notch and supported for relative movement with respect to said secure magnetic plate, sai-d conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

5, An electromagnetic latch operating mechanism comprising a relatively thin magnetic plate formed with a notch tapering inwardly from an outer edge thereof, u conductor oriented substantially perpendicularly of said magnetic plate and disposed within said notch for relative movement with respect to said magnetic plate, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

6. An electromagnetic latch operating mechanism comprising a magnetic plate formed with a notch tapering inwardly from an outer edge thereof, a conductor disposed in said notch in non-contacting relationship with and substa'ntially perpendicular to said magnetic plate and arranged for movement substantially in the direction of said taper, and means for directing electric current through said conductor for establishing a magnetic field partially extending through said magnetic plate, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

7. An electromagnetic latch operating mechanism comprising a plurality of magnetic plates each formed with a notch tapering inwardly from an outer edge thereof, means rigidly supporting said magnetic plates in parallel relationship, and a movable conductor disposed within said notches in said magnetic plates and in non-contacting relationship therewith, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

8. An electromagnetic latch operating mechanism cornprising a plurality of like, relatively thin plates cach formed of magnetic material and each having a V-shaped notch therein inwardly tapering from an outer edge thereof to a vertex disposed centrally of said plate; means rigidly securing said plates in parallel relationship with aligned notches thereby defining a substantially V-shaped air gap, and a pivotally supported conductor extending through said V-shaped air gap in non-contacting relationship therewith whereby upon the application of current to said conductor, the magnetic iield thereby created interacts with said magnetic plates to cause said conductor to pivot inwardly in said V-shaped air gap, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

9. An electromagnetic latch operating mechanism comprising a plurality of like relatively thin plates each formed of magnetic material and each having a V-haped notch therein inwardly tapering from an outer edge thereof to a vertex disposed centrally of said plate; means rigidly securing said plates in parallel and mutually spaced relationship with aligned notches thereby defining a substantially V-shape'd air gap, and a pivotally supported conductor extending through said V-shaped air gap in non-contacting relationship therewith whereby upon the application of current to said conductor, the magnetic field thereby created interacts with said magnetic plates to cause said conductor to pivot inwardly in said V-shaped air gap, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

l0. An electric circuit interrupter comprising, within a structural framework, a pair of current interrupting contacts; means including an arm for engaging and disengaging said contacts; a conductor pivotally secured to said framework and providing at one end thereof a latch for retaining said contacts in engaged position; and a magnetic structure secured to said framework and formed with a substantially V-shaped air gap encompassing said conductor whereby upon the passage of a current in excess of some predetermined value through said conductor, said conductor is drawn further into said V-shaped air gap for delatching said contact engaging means.

ll. An electric circuit interrupter comprising, within a structural framework, a pair of current interrupting contacts, means including an arm for engaging and disengaging said contacts; a conductor pivotally secured to sai-d framework and providing at one end thereof a latch for retaining said contacts in engaged position; and a magnetic structure secured to said framework; said magnetic structure being formed of a plurality of parallel magnetic plates; each of said plates having a notch inwardly tapering from an outer edge; said magnetic structure being so arranged that said notches in said plates substantially enclose said conductor; said magnetic structure being formed with a substantially V-shaped air gap encompassing said conductor whereby upon the passage of a current in excess of some predetermined value through said conductor, said conductor is drawn further into said V-shaped air gap for delatching said contact engaging means.

12. An electric circuit interrupteicomprising, within a structural framework, a pair of current interrupting contacts, means including an arm for engaging and disengaging said contacts, a magnetic structure secured to said framework and formed with a plurality of parallel and mutually spaced magnetic plates each having a mutually aligned V-shaped notch therein tapering inwardly from an outer edge of the plate, a conductor pivotally secured at one end thereof to said structural framework and arranged at the other end thereof to provi-de a latch for normally retaining said arm in the Contact engaged position, means normally biasing said arm toward the contact disengaged position, means for directing current ow through said contact when in the engaged position in sexies through said conductor, said conductor and magnetic structure being mutually arranged whereby upon the passage through said conductor of a current in excess of some predetermined value, said conductor is drawn further into said notches in said magnetic plate thereby pivoting on said framework and delatching said arm to permit contact disengagement under the intluence of said bias means.

13. An electromagnetic latch operating mechanism comprising a magnetic member formed with a tapered opening therein and a bimetallic conductor disposed for movement within said opening relative to said magnetic member, said conductor operatively connected to a latch mechanism to cause operation thereof at a predetermined point.

14. An electric circuit interrupter comprising, within a structural framework, a pair of current interrupting contacts, means including an arm for engaging and disengaging said contacts, a conductor formed of a union of dissimilar metals adapted to change in configuration under the inuence of heat pivotally secured to said framework and providing at one end thereof a latch for retaining said contacts in engaged position, and a magnetic structure secured to said framework and formed with a substantially V-shaped air gap encompassing said con ductor whereby upon the passage of a current in excess of some predetermined value through said conductor, said conducto-r is drawn fur-ther into said V-shaped air gap for delatching said contact engaging means.

15. An electric circuit interrupter comprising within a structural framework, a pair of current interrupting contacts, means including an arm for engaging and disengaging said contacts, a magnetic structure secured to said framework and formed with a plurality of parallel and mutually spaced magnetic plates each having a mutually aligned V-shaped notch therein tapering inwardly from an outer edge of the plate, a conductor pivotally secured at one end thereof to said structural framework and arranged at the other end thereof to provide a latch Ifor normally retaining said arm in the contact engaged position, means normally biasing said arm toward the contact disengaged position, means for directing current ilow through said contacts when in the engaged position in series through said conductor, said conductor and magnetic structure being mutually arranged whereby upon the passage through said conductor of a current in excess of some predetermined value, said conductor is drawn further into said notches in said magnetic plate thereby pivoting on said framework and delatching said army to permit contact disengagement under the inuence of said bias means, said conductor being formed of at least two dissimilar substances arranged whereby under the influence of heat, said conductor bends into said notches thereby delatching said arm independently of the magnetic action of said magnetic structure.

References Cited in the le of this patent UNITED STATES PATENTS 1,628,115 Call May l0, 1927 1,763,502 Branchu June 10, 1930 2,037,570 Forsberg Apr. 14, 1936 FOREIGN PATENTS 165,563 Great Britain July 7, 1921 337,162 Great Britain Oct. 30, 1930 

